HVAC modules in automobiles typically have an inlet for allowing air into the module (often from a blower), outlets for controlling exit of air from the HVAC into the automobile interior, an evaporator for selectively cooling the air passing through the module and a heater core for selectively warming air passing through the module. In order to provide desirable temperature conditions within the vehicle interior, means for selecting and mixing warm air from the heater core and cool air from the evaporator are required.
The mixing operation is typically performed using a pair of doors which can regulate the relative amounts of cool air and warm air which mix to provide the resultant flow output. A problem with current systems is that the cool air and warm air often do not mix properly before the flow of air is expelled into the vehicle interior. This results in inefficiency and can lead to undesirable temperature conditions within the automobile interior. Another problem with typical systems is that when either full hot mode (where no cool air is required) or full cold mode (where no warm air is required) is selected, there is often a small amount of leakage of the undesired air into the stream. This leads to the module outputting either slightly warmer or slightly cooler air than would otherwise be possible.